Migrate NIS users and groups into LDAP

yum install openldap-servers

cd /usr/share/openldap/migration

run the migration scripts

verify document signatures

Verify the signature
#gpg --output document --decrypt document.sig

sign documents

Sign the document
#gpg --output document.sig --sign document

decrypt documents

Decrypt a document

#gpg --output document --decrypt document.gpg

encrypt documents

To encrypt you will need to have the persons public key available to you so you can import it

#gpg --import public-key.gpg

Encrypt a document

#gpg --output document.gpg --encrypt --recipient username@example.com document

generate key pairs

Generate the key pairs using the following command
#gpg --gen-key

use the Real-time Blackhole List (RBL) via DNS

Sendmail

Edit /etc/mail/sendmail.mc and add

FEATURE(`dnsbl', `dnsbl.example.com', `you have been rejected mofo')dnl

#make -C /etc/mail

#service sendmail restart

Postfix

#postconf -e "smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination, reject_rbl_client dnsbl.example.com"

#service postfix restart